1. Field of the Invention
The present general inventive concept relates to an energy effective switching power supply apparatus and an energy effective method thereof. More particularly, the present general inventive concept relates to an energy effective switching power supply apparatus and an energy effective method thereof that saves energy by improving power efficiencies of an SMPS (Switching Mode Power Supply) used as a switching power apparatus in electronics appliances.
2. Description of the Related Art
Generally, an SMPS (Switching Mode Power Supply) is used as a switching power supply apparatus in an image forming apparatus, such as a printer. The SMPS refers to an apparatus that rectifies an AC (alternating current) voltage externally input and supplies the rectified voltage to each part of an electronics appliance.
The SMPS reduces power loss by having a switching device operating in a switching mode to reduce power loss, and is compact-sized by use of a high frequency power transformer. The SMPS is designed to simultaneously output DC voltages (Direct current) having different amplitudes. For example, it is possible to simultaneously output DC voltages of 3.3V or 5V supplied to a main power supply in a printer, and a DC voltage of 24V supplied to a HVPS (High Voltage Power Supply) and a printing engine part.
FIG. 1 illustrates a conventional switching power supply apparatus.
Referring to FIG. 1, the switching power supply apparatus includes an external power inputting part 10, a rectifying part 20, a switching controlling part 30, a power transforming part 40, a first power outputting part 50, a second power outputting part 60, and a feedback circuit part 70.
The external power inputting part 10 receives an AC power from an external power supply (not shown) as an input. The rectifying part 20 rectifies the input AC power using a bridge diode (not shown) and a capacitor (not shown), and outputs a DC power. The DC power output from the rectifying part 20 is supplied to a first coil of a power transformer of the power transforming part 40, and the power transforming part 40 induces a voltage to a second coil by interactions between the first coil and the second coil.
The switching controlling part 30 interrupts electric current flowing in the first coil of the power transforming part 40 and controls the voltage induced to the second coil of the power transforming part 40. The voltage induced to the second coil of the power transforming part 40 is rectified and smoothed by a first power outputting part 50 and a second power outputting part 60, respectively. The first power outputting part 50 outputs a first DC voltage Va as a first output voltage, and the second power outputting part 60 outputs a second DC voltage Vb as a second output voltage.
The switching controlling part 30 has a PWM-IC (Pulse Width Modulation-integrated Circuit) 35, and the PWM-IC 35 is connected to the first coil of the power transforming part 40 through a transistor TR1. An OUT terminal of the PWM-IC 35 turns on/off the transistor TR1, interrupts the current flowing in the first coil and controls the voltage induced to the second coil of the power transforming part 40.
A diode D1, a resistance R1, and a first capacitor C1 rectify and smooth a current flowing in an auxiliary coil of the power transforming part 40 and supply an operating power to a Vcc terminal of the PWM-IC 35. A switching frequency is determined with respect to the transistor TR1 output to the OUT terminal by a capacitance of a second capacitor C2 connected to a CT terminal of the PWM-IC 35.
The feedback circuit part 70 senses the second output voltage of the second power outputting part 60 and transmits a feedback signal to an FB terminal of the PWM-IC 35. An operation of the PWM-IC 35 is determined according to the transmitted feedback signal. That is, when the second output voltage of the second power outputting part 60 is higher than a reference voltage, the feedback circuit part 70 transmits a feedback signal instructing the PWM-IC 35 to stop operating.
Likewise, the conventional switching power supply apparatus switches the transistor TR1 ON or OFF at a uniform frequency all the time, regardless of changes of the first and second output voltages Va and Vb, respectively, and accordingly, a switching loss is incurred and unnecessary power consumption occurs. If an output current of the first power outputting part 50 rises, the second output voltage of the second power outputting part 60 rises by cross regulation, and an apparatus that is supplied with the second output voltage by the second power outputting part 60 may be damaged by the increase in the second output voltage.